DIFFERENT TYPES OF IRRIGATION AND IRRIGATION SYSTEMS STORAGE
- Irrigation is the artificial application of water to the land or soil. It is the replacement or supplementation of rainwater with another source of water. It is used in dry areas and during periods of inadequate rainfall.
- The main idea behind irrigation systems is to:
- Assist in the growing of agricultural crops and plants by maintaining with the minimum amount of water required.
- maintenance of landscapes
- Revegetation of disturbed soils.
- Additionally, irrigation also has a few other uses in crop production, which include:
- protecting plants against frost
- suppressing weed growth in grain fields\
- Preventing soil consolidation.
- for dust suppression,
- Disposal of sewage, and in mining.
- In contrast, agriculture that relies only on direct rainfall is referred to as rain-fed or dryland farming.
- Irrigation is often studied together with drainage, which is the natural or artificial removal of surface and sub-surface water from a given area.
IRRIGATION IN INDIA
- In India, the irrigated area consists of about 36 per cent of the net sown area. Presently, the agricultural sector accounts for about 83 per cent of all water uses.
- There are various types of systems of irrigation practices in different parts of India. Various types of irrigation techniques differ in how the water obtained from the source is distributed within the field. In general, the goal is to supply the entire field uniformly with water, so that each plant has the amount of water it needs, neither too much nor too little.
- Irrigation in India is carried on through wells, tanks, canals, Perennial canal, Multi-purpose river valley projects, etc.
WELL AND TUBE WELL IRRIGATION
- A well is a hole dug in the ground to obtain the subsoil water. An ordinary well is about 3-5 metres deep but deeper wells up-to 15 metres are also dug.
- This method of irrigation has been used in India from time immemorial. Various methods are used to lift the ground water from the well for irrigation, drinking, bathing and for other purposes.
- Well irrigation is more popular in those regions where ground water is in plenty and where there are few canals. These areas include a large part of the Great Northern Plain, the deltaic regions of the Mahanadi, the Godavari, the Krishna and the Cauvery, parts of the Narmada and the Tapi valleys and the weathered layers of the Deccan Trap and crystalline rocks and the sedimentary zones of the Peninsula.
- However, the greater part of the Penisnular India is not suitable for well irrigation due to rocky structure, uneven surface and lack of underground water. Large dry tracts of Rajasthan, the adjoining parts of Punjab, Haryana, and Gujarat and some parts of Uttar Pradesh have brackish ground water which is not fit for irrigation and human consumption and hence unsuitable for well irrigation.
- There were about 5 million wells in 1950-51 and their number has now increased to about 12 million. Well irrigation accounts for more than 60 per cent of the net irrigated area in the country against 29.2 per cent of canal and only 4.6 per cent of tank irrigation. It accounted 59.78 lakh hectares in 1950-51 which rose to about 332-77 lakh hectares in 2000-01 thereby registering more than fivefold increase in well irrigation.
- Uttar Pradesh has the largest area under well irrigation which accounts for about 28 per cent of the well irrigated area of India. This is followed by Rajasthan (10%), Punjab (8.65%), Madhya Pradesh (8%), and Gujarat (7.3%).
- In Gujarat, about 82 per cent of the net irrigated area is under well irrigation. The other states where well irrigation plays a significant role are Punjab (80%), Uttar Pradesh (74%), Rajasthan (71%), Maharashtra (65%), Madhya Pradesh (64 %) and West Bengal (60%)
- Uttar Pradesh, Rajasthan, Punjab, Madhya Pradesh, Gujarat, Bihar and Andhra Pradesh account for three-fourths of the total well irrigated area of India.
A) Tube well
- A tube well is a deeper well (generally over 15 metres deep) from which water is lifted with the help of a pumping set operated by an electric motor ,a diesel engine or solar power.
- A tube well cannot be constructed everywhere and requires some geographical conditions favouring its installation. The main factors are:
- There should be sufficient quantity of ground water because a tube well can generally irrigate 2 hectares per day against 0.2 hectares per day irrigated by an ordinary well.
- The water level should be nearly 15 metres. If the water table is more than 50 metres deep the cost of pumping out water from the tube well becomes uneconomic.
- There should be regular supply of cheap electricity or diesel so that water from the tube well can be taken out at the hour of need.
- The soil in the immediate neighbourhood of the tube-well should be fertile so that there is demand for irrigation and the cost involved in the construction and operation of the tube well can be recovered by the increased farm production.
- The first tube well of India was sunk in Uttar Pradesh in 1930. Till 1951 India had just 2,500 tube wells. The central and the state governments are helping the farmers by distributing pumping sets, granting loans and giving subsidies. The number of electrical pumpsets/tube wells increased from 2 lakh in 1960 to over 4 million in 1995-96 while the dieselized pumpsets increased from 2 3 lakh to about 3 million during the same period.
- In several areas, the ‘persian wheel’ earlier used for lifting water has been replaced by tube wells.
- Tamil Nadu with 11 lakh tube wells has the largest number in the country followed by Maharashtra (9 lakh), Andhra Pradesh (6.7 lakh), Uttar Pradesh (5.3 lakh), Madhya Pradesh (4.6 lakh), Karnataka (4.4 lakh), Punjab (3.9 lakh) and Haryana (3.5 lakh). Thus more than three-fourths of India’s tube wells are functioning in Tamil Nadu, Maharashtra, Andhra Pradesh, Uttar Pradesh, Madhya Pradesh, Karanataka and Punjab.
B) Merits of Well and Tube Well Irrigation:
- Well is simplest and cheapest source of irrigation and the poor Indian farmer can easily afford it.
- Well is an independent source of irrigation and can be used as and when the necessity arises. Canal irrigation, on the other hand, is controlled by other agencies and cannot be used at will.
- Excessive irrigation by canal leads to the problem of reh which is not the case with well irrigation.
- There is a limit to the extent of canal irrigation beyond the tail end of the canal while a well can be dug at any convenient place.
- Several chemicals such as nitrate, chloride, sulphate, etc. are generally found mixed in well water. They add to the fertility of soil when they reach the agricultural field along with well water.
- The farmer has to pay regularly for canal irrigation which is not the case with well irrigation.
- More reliable during periods of drought when surface water dries up.
- Suitable for smallholdings.
C) Demerits of Well and Tube Well Irrigation:
- Only limited area can be irrigated. Normally, a well can irrigate 1 to 8 hectares of land.
- The well may dry up and may be rendered useless for irrigation if excessive water is taken out
- In the event of a drought, the ground water level falls and enough water is not available in the well when it is needed the most.
- Tubewells can draw a lot of groundwater from its neighbouring areas and make the ground dry and unfit for agriculture.
- Well and tube well irrigation is not possible in areas of brackish groundwater.
- Lack of electricity, diesel and requirement of capital investment for Tubewell
- Agriculture Ministry will provide financial assistance of up to Rs 57,600 on purchase of solar energy pumps used for irrigation by farmers. Solar energy-driven pumping set is a viable alternative for electrical and diesel pumping systems in farm irrigation. Therefore, it has been included in the list of farm equipment that get assistance under central scheme.
- Agriculture Ministry, with consensus of the New and Renewable Energy Ministry, has introduced solar energy pumping systems under the ‘Sub Mission on Agriculture Mechanization’ implemented through state governments.
- Canals used to be the most important source of irrigation up-to 1960s, but in the 1970s they yielded first place to wells and tube wells and now constitute the second most important source of irrigation in India.
- The percentage of canal irrigation area to total irrigated area in the country has fallen from about 39.77 per cent in 1950-51 to 29 per cent in 2000-01.
- Canals can be an effective source of irrigation in areas of low level relief, deep fertile soils, perrenial source of water and extensive command area. Therefore, the main concentration of canal irrigation is in the northern plain of India, especially the areas comprising Uttar Pradesh Haryana and Punjab.
- The digging of canals in rocky and uneven areas is difficult and uneconomic. Thus the canals are practically absent from the Peninsular plateau area. However, the coastal and the delta regions in South India do have some canals for irrigation.
- Canals in India are of two types:
- Inundation canals, which are taken out from the rivers without any regulating system like weirs etc. at their head. Such canals provide irrigation mainly in the rainy season when the river is in flood and there is excess water. When the rainy season is over, the flood in the river subsides, the level of water falls below the level of the canal head and the canal dries up. Some canals taken off from the Satluj in Punjab were of this type. Since irrigation from this type of canals is uncertain, they have been converted in perennial canals.
- Perennial Canals are those which are taken off from perennial rivers by constructing a barrage across the river. Most of the canals in India today are perennial.
- The net area under canal irrigation is about 15.8 million hectares. The main canal irrigated areas are in the northern plains of India where Uttar Pradesh, Punjab, Haryana, Rajasthan and Bihar account for about 60 per cent of the canal irrigated area of the country.
- In south and central India, Andhra Pradesh, Maharasthra, Karnataka, Madhya Pradesh, Chhattisgarh, Orissa and Tamil Nadu are important states of canal irrigation.
- Uttar Pradesh has above 30 lakh hectares under canal irrigation which is 31 per cent of the total canal irrigated area of the country. Over one-fourth of the net irrigated area of the state is irrigated by canals.
- In early days, canal irrigation accounted for about 40 per cent of the total irrigated area in Punjab but the share of canal irrigation fell down to less than 19 per cent in 2000-01.
- Haryana depends upon canal irrigation for its agricultural prosperity to a great extent. About 50 per cent of the irrigated area in Haryana is irrigated by canals. This is the second highest percentage for any state after Chhattisgarh.
- With 17 lakh hectares under canal irrigation i.e. 10 % of the total canal irrigated area of India, Andhra Pradesh is next only to Uttar Pradesh and tops in South India in so far as area under canal irrigation is concerned. Canal irrigation accounts for about 37 per cent of the net irrigated area of the state.
A) Merits of Canal Irrigation:
- Most of the canals provide perennial irrigation and supply water as and when needed. This saves the crops from drought conditions and helps in increasing the farm production.
- Canals carry a lot of sediment brought down by the rivers. This sediment is deposited in the agricultural fields which add to the fertility of soil.
- Some of the canals are parts of multipurpose projects and, therefore, provide cheap source of irrigation.
- Although the initial cost involved in canal irrigation is much higher, it is quite cheap in the long run.
B) Demerits of Canal Irrigation:
- The canal water soaks into the ground and leads to the problem of water-logging along the canal route.
- Excessive flow of water in the fields raises the ground water level. Capillary action brings alkaline salts to the surface and makes large areas unfit for agriculture. Vast areas in Panjab, Haryana and Uttar Pradesh suffer from the problem of ‘reh’ caused by canal irrigation. About 36,000 hectares have been rendered useless in Nira Valley of Maharashtra due to high concentration of salts in the soil resulting from canal irrigation.
- The marshy areas near the canals act as breeding grounds of mosquitoes which result in widespread malaria.
- Many canals overflow during rainy season and flood the surrounding areas.
- Canal irrigation is suitable in plain areas only.
- A tank consists of water storage which is developed by constructing a small bund of earth or stones built across a stream. The water impounded by the bund is used for irrigation and for other purposes. Some tanks are built partly as dugouts and partly by enclosing bunds.
- Tanks are of varying size but most of the tanks are of small size and are built by individual farmers or groups of farmers. There are about 5 lakh big and 50 lakh small tanks irrigating over 25.24 lakh hectares of agricultural land.
- The ratio of tank irrigated land to the total irrigated area of the country has reduced from 14 per cent in the 1960-61 to about 4.6 per cent in 2001-01, primarily due to increase in well and tube well irrigation and partly due to fall in the tank irrigation .
- Tank irrigation is popular in the peninsular plateau area where Andhra Pradesh (Including Telangana) and Tamil Nadu are the leading states.
- Andhra Pradesh is the largest state of tank irrigation which has about 29 per cent of tank irrigated area of India. About 16 per cent of the total irrigated area of the state is irrigated by tanks. The drainage areas of the Godavari and its tributaries have large number of tanks. Nellore and Warangal are the main districts of tank irrigation.
- Tamil Nadu has the second largest area which is over 23 per cent of tank irrigated area of India and about one-fifth of the total irrigated area of the state. There are about 24,000 tanks in Tamil Nadu.
- Tanks comprise an important source of irrigation in the Karnataka Plateau, eastern Madhya Pradesh, eastern Maharashtra, interior Orissa and Kerala.
- Outside the Peninsular plateau, West Bengal, Bihar, Bundelkhand area of Uttar Pradesh, Rajasthan and Gujarat have tank irrigation.
A) The tank irrigation is practised mainly in peninsular India because:
- The undulating relief and hard rock’s make it difficult to dig canals and wells.
- There is little percolation of rain water due to hard rock structure and ground water is not available in large quantity.
- Most of the rivers of this region are seasonal and dry up in summer season. Therefore, they cannot supply water to canals throughout the year.
- There are several streams which become torrential during rainy season. The only way to make best use of this water is to impound it by constructing bunds and building tanks. Otherwise this water would go waste to the sea.
- The scattered nature of population and agricultural fields also favours tank irrigation.
B) Merits of Tank Irrigation:
- Most of the tanks are natural and do not involve heavy cost for their construction. Even an individual farmer can have his own tank.
- Tanks are generally constructed on rocky bed and have longer life span.
- In many tanks, fishing is also carried on. This supplements both the food resources and income of the farmer.
C) Demerits of Tank Irrigation:
- Many tanks dry up during the dry season and fail to provide irrigation when it is needed the most.
- Silting of the tank bed is a serious problem and it requires desilting of the tank at regular intervals.
- Much water is evaporated from the large expanse of shallow water and is thus not available for irrigation.
- Tanks cover large areas of cultivable land. In many areas, other sources of irrigation have been adopted and the dry beds of tanks have been reclaimed for agriculture.
- Moreover, lifting of water from tanks and carrying it to the fields is a strenuous and costly exercise which discourages the use of tanks as a source of irrigation.
- In traditional surface irrigation methods, the losses in water conveyance and application are large. These losses can be considerably reduced by adopting drip and sprinkler irrigation methods.
- Among all the irrigation methods, the drip irrigation is the most efficient and it can be practised in a large variety of crops, especially in vegetables, orchard crops, flowers and plantation crops.
- In drip irrigation, water is applied near the plant root through emitters or drippers, on or below the soil surface, at a low rate varying from 2 – 20 litres per hour. The soil moisture is kept at an optimum level with frequent irrigations.
- Drip irrigation results in a very high water application efficiency of about 90-95 per cent.
- The drip system was developed for field crops in Israel in the early 1960s. The area under drip irrigation system in the USA is about 1 M ha, followed by India, Spain, Israel, etc.
- In India, there has been a tremendous growth in the area under drip irrigation during the last 15 years. At present, around 3.5 lakh ha area is under drip irrigation with the efforts of the Government of India. Maharashtra (94,000 ha), Karnataka (66,000 ha) and Tamil Nadu (55,000 ha) are some of the states where large areas have been brought under drip irrigation. Many crops are irrigated by the drip method in India with the tree crops occupying the maximum percentage of the total area under drip irrigation, followed by vine crops, vegetables, field crops, flowers and other crops.
- The National Committee on Plasticulture Applications in Horticulture (NCPAH), Ministry of Agriculture, Government of India, has estimated a total of 27 million hectares area in the country that has the potential of drip irrigation application.
A) The advantages of drip irrigation are:
- Possibility of using soluble fertilizers and chemicals
- Fertilizer and nutrient loss is minimized due to localized application and reduced leaching.
- Water application efficiency is high
- Field levelling is not necessary. Fields with irregular shapes are easily accommodated.
- Recycled non-potable water can be safely used.
- Soil type plays less important role in frequency of irrigation.
- Soil erosion is lessened.
- Weed growth is lessened.
- Water distribution is highly uniform, controlled by output of each nozzle.
- Labour cost is less than other irrigation methods.
- Variation in supply can be regulated by regulating the valves and drippers.
- Foliage remains dry, reducing the risk of disease.
- Usually operated at lower pressure than other types of pressurised irrigation, reducing energy costs.
B) The disadvantages of drip irrigation are:
- Initial cost can be more.
- The sun can affect the tubes used for drip irrigation, shortening their usable life.
- If the water is not properly filtered and the equipment not properly maintained, it can result in clogging.
- For subsurface drip the irrigator cannot see the water that is applied. This may lead to the farmer either applying too much water (low efficiency) or an insufficient amount of water, this is particularly common for those with less experience with drip irrigation.
- Drip irrigation might be unsatisfactory if herbicides or top dressed fertilizers need sprinkler irrigation for activation.
- Drip tape causes extra clean up costs after harvest. Users need to plan for drip tape winding, disposal, recycling or reuse.
- Waste of water, time and harvest, if not installed properly. These systems require careful study of all the relevant factors like land topography, soil, water, crop and agro-climatic conditions, and suitability of drip irrigation system and its components.
- In lighter soils subsurface drip may be unable to wet the soil surface for germination. Requires careful consideration of the installation depth.
- One of the main purpose of drip irrigation is to reduce the water consumption by reducing the leaching factor. However when the available water is of high salinity or alkalinity, the field soil becomes gradually unsuitable for cultivation due to high salinity or poor infiltration of the soil. Thus drip irrigation converts fields in to fallow lands when natural leaching by rain water is not adequate in semi arid and arid regions.
- Most drip systems are designed for high efficiency, meaning little or no leaching. Without sufficient leaching, salts applied with the irrigation water may build up in the root zone. On the other hand, drip irrigation avoids the high capillary potential of traditional surface-applied irrigation, which can draw salt deposits up from deposits below.
- Drip irrigation systems cannot be used for damage control by night frosts (like in the case of sprinkler irrigation systems)
- In the sprinkler method of irrigation, water is sprayed into the air and allowed to fall on the ground surface somewhat resembling rainfall. The spray is developed by the flow of water under pressure through small orifices or nozzles. The pressure is usually obtained by pumping. With careful selection of nozzle sizes, operating pressure and sprinkler spacing the amount of irrigation water required to refill the crop root zone can be applied nearly uniform at the rate to suit the infiltration rate of soil.
- Nearly all crops are suitable for sprinkler irrigation system except crops like paddy, jute, etc. The dry crops, vegetables, flowering crops, orchards, plantation crops like tea, coffee are all suitable and can be irrigated through sprinklers.
- The sprinkler irrigation system is a very suitable method for irrigation on uneven lands and on shallow soils. It is best suited to coarse sandy terrain where the percolation loss is more and where as a consequence, the frequency of irrigation required is more. The sprinkler irrigation system is also suitable in undulating terrain where land shaping is expensive or technically not feasible. The removal of fertile soil cover by land shaping is not advisable. Sprinkler irrigation system can also be adopted in hilly regions where plantation crops are grown.
- Though sprinkler irrigation system is known since 1946, yet the farmers started adopting it in large scale only since 1980s. It started in the hilly areas of Western ghats in states of Kerala, Tamil Nadu and Karnataka and in the North eastern states mainly for plantation crops like coffee, tea, cardamom, rubber etc. Slowly it spreads to the water scarcity and light soil states of Rajasthan and Haryana in addition to the black soil area of Madhya Pradesh.
- Madhya Pradesh contributes 1.5 lakhs hectare which is almost 25 per cent of the total area under sprinkler in the country(6.7 lakh hectares). This is followed by West Bengal, Assam, Haryana and Rajasthan.
- The potential for coverage under sprinkler irrigation is estimated to be about 42.5 million ha. Government of India has taken an initiative to give subsidy to the farmers to an extent even upto 50% in order to popularize this method of water application.
A) Advantages of sprinkler irrigation
- Elimination of the channels for conveyance, therefore no conveyance loss
- Suitable to all types of soil except heavy clay
- Suitable for irrigating crops where the plant population per unit area is very high. It is most suitable for oil seeds and other cereal and vegetable crops
- Water saving
- Closer control of water application convenient for giving light and frequent irrigation and higher water application efficiency
- Increase in yield
- Mobility of system
- May also be used for undulating area
- Saves land as no bunds etc. are required
- Influences greater conducive micro-climate
- Areas located at a higher elevation than the source can be irrigated
- Possibility of using soluble fertilizers and chemicals
- Less problem of clogging of sprinkler nozzles due to sediment laden water
- The overall cost of labour is generally reduced.
- Erosion of soil cover which is common in surface irrigation can be eliminated.
B) Disadvantages of sprinkler system:
- Higher initial cost.
- High and continuous energy requirement for operation.
- Under high wind condition and high temperature distribution and application efficiency is poor.
- Highly saline water causes leaf burning when temperature higher than 95 F.
- When lands have been already leveled and developed for surface or other irrigation methods sprinkler irrigation is not so economical.
- Loss of water due to evaporation from the area during irrigation.
- Above canopy sprinkling may cause washing of spray, materials and aggravate the incidence
- Furrow irrigation is a type of surface irrigation in which trenches or “furrows” are dug between crop rows in a field. Farmers flow water down the furrows (often using only gravity) and it seeps vertically and horizontally to refill the soil reservoir. Flow to each furrow is individually controlled.
- Furrow irrigation works well for row crops, tree crops and, because water does not directly contact the plants, crops that would be damaged by direct inundation by water such as tomatoes, vegetables, potatoes and beans.
- One of the oldest methods of irrigation, furrow irrigation is cheap and low-tech making it particularly attractive in the developing world or places where mechanized spray irrigation is unavailable or impractical.
- One of the difficulties of furrow irrigation is ensuring uniform dispersion of water over a given field. In order to address this problem, some farmers engage in field leveling to remove any small hills that would have been bypassed by the gravity flow of the water.
- Another difficulty with furrow irrigation is the increased potential for water loss due to runoff (although water loss to evaporation is less relative to mechanized spray irrigation). Building retention ponds along the edges of fields can help capture this runoff, allowing it to be pumped back to the upslope side of the field for use in further irrigation cycles.
OTHER TYPES OF IRRIGATION
A) Surge Irrigation
- Surge Irrigation is a variant of furrow irrigation where the water supply is pulsed on and off in planned time periods (e.g. on for 1 hour off for 1½ hour). The wetting and drying cycles reduce infiltration rates resulting in faster advance rates and higher uniformities than continuous flow.
B) Ditch Irrigation
- Ditch Irrigation is a rather traditional method, where ditches are dug out and seedlings are planted in rows. The plantings are watered by placing canals or furrows in between the rows of plants. Siphon tubes are used to move the water from the main ditch to the canals.
C) Sub-irrigation or seepage irrigation
- It is a method of irrigation where water is delivered to the plant root zone from below the soil surface and absorbed upwards. The excess may be collected for reuse.
- Subirrigation is used in growing field crops such as tomatoes, peppers, and sugar cane in areas with high water tables.
- Advantages are water and nutrient conservation, and labor-saving. The outfitting cost is relatively high. Potential problems, such as the possibility of increased presence of disease in recycle water.
PROBLEMS RELATED TO IRRIGATION
- Competition for surface water rights.
- Depletion of underground aquifers.
- Ground subsidence
- Under-irrigation or irrigation giving only just enough water for the plant (e.g. in drip line irrigation) gives poor soil salinity control which leads to increased soil salinity with consequent build up of toxic salts on soil surface in areas with high evaporation. This requires either leaching to remove these salts and a method of drainage to carry the salts away. When using drip lines, the leaching is best done regularly at certain intervals (with only a slight excess of water), so that the salt is flushed back under the plant’s roots.
- Over-irrigation because of poor distribution uniformity or management wastes water, chemicals, and may lead to water pollution.
- Deep drainage (from over-irrigation) may result in rising water tables which in some instances will lead to problems of irrigation salinity requiring water table control by some form of subsurface land drainage.
- Irrigation with saline or high-sodium water may damage soil structure owing to the formation of alkaline soil.
- (Think more points from the chapter)